this is how i do it...
go to the airlines website and find the link to email them.
write the email the night your return flight gets back or the next morning. (they'll think you're more pissed sicne you complained so quickly)
my emails usually look like this....
Dear _____ Airlines Representative,
I am a frequent traveller who recently purchased roundtrip tickets from _______ to _______ through your airline. (give cities and flight numbers)
then i go on to complain about anything and everything. whether it be departure/arrival time being late, delays, temp in the plane, service, boarding procedures, etc.
then...
While I was pleased with the convenience and accessibility of using your airline I'm disappointed in the difficulties that occurred because of _____. I would enjoy the oppurtunity to fly through your airline again, blah blah blah. (just be courteous)
so do you have any idea how much a standby ticket might be?